Electromagnon excitation in the field-induced noncollinear ferrimagnetic phase ofBa2Mg2Fe12O22studied by polarized inelastic neutron scattering and terahertz time-domain optical spe

Abstract

We have studied magnetic excitations in a field-induced noncollinear commensurate ferrimagnetic phase of Ba 2 Mg 2 Fe 12 O 22 by means of polarized inelastic neutron scattering (PINS) and terahertz (THz) time-domain optical spectroscopy under magnetic field. A previous THz spectroscopy study reported that the field-induced phase exhibits electric-dipole-active excitations with energies of around 5 meV [Kida et al., Phys. Rev. B 83, 064422 (2011)]. In the present PINS measurements, we observed inelastic scattering signals around 5 meV at the zone center in the spin-flip channel.This directly shows that the electric-dipole-active excitations are indeed of magnetic origin, that is, electromagnons. In addition, the present THz spectroscopy confirms that the excitations have oscillating electric polarization parallel to the c axis. In terms of the spin-current model (KatsuraNagaosa-Balatsky model), the noncollinear magnetic order in the field-induced phase can induce static electric polarization perpendicular to the c axis, but not dynamic electric polarization along the c axis. We suggest that the electromagnon excitations can be explained by applying the magnetostriction model to the out-of-phase oscillations of the magnetic moments, which is deduced from the present experimental results.

Magnetic structures and excitations in a multiferroic Y-type hexaferrite BaSrCo2Fe11AlO22

“…A previous THz spectroscopy study by Kida et al has revealed that another Y-type hexaferrite Ba 2 Mg 2 Fe 12 O 22 (BMFO) exhibits electric-field-active magnetic excitation, which is referred to as electromagnon 15,16 . Nakajima et al have recently performed inelastic polarized neutron scattering (IPNS) measurements on BMFO 17 , confirming that the excitation is indeed of magnetic origin and that the magnetic excitation leads to oscillating electric polarization along the c axis via the mangetostriction mechanism.…”

“…As mentioned in the introduction, the Y-type hexaferrite BMFO is known to exhibit electromagnon excitation [15][16][17] . Thus, we expect that BSCoFAO also exhibits the electricfield-active magnon excitation, and that it would be applicable for magnetically-tunable light absorption devices working at room temperature.…”

“…The multiferroic hexaferrites have also attracted attention in terms of dynamical spinpolarization coupling [15][16][17] . A previous THz spectroscopy study by Kida et al has revealed that another Y-type hexaferrite Ba 2 Mg 2 Fe 12 O 22 (BMFO) exhibits electric-field-active magnetic excitation, which is referred to as electromagnon 15,16 .…”

Electromagnon in theZ-type hexaferrite(BaxSr1−x)3Co2Kadlec1, Kadlec2, Vít3 et al. 2016Phys. Rev. B28080View full textAdd to dashboardCite

“…Note that in both Z-and Y-type hexaferrites, the static polarization P appears due to the inverse Dzyaloshinskii-Moriya interaction 2,8 perpendicularly to the z axis, if one applies an external magnetic field H ⊥ z whereby the transverse conical structure is stabilized. 3,19 However, the magnetic structure of the Y -type hexaferrite is longitudinally conical at µ 0 H = 0 T , 17,18 whereas that of the Z-hexaferrite at zero and small magnetic fields is transverse conical. The electromagnons in both materials share several features: (i) they are active in E ω z even in zero magnetic field, (ii) their frequencies shift with external magnetic field and, finally, (iii) they disappear from the spectra above some threshold magnetic field, when the transverse or longitudinal conical magnetic structures disappear.…”

“…As regards the hexaferrites, an electromagnon was reported only in the Y -type compound Ba 2 Mg 2 Fe 12 O 22 . [17][18][19] Interestingly, it was observed not only in the spin-induced FE phase below 50 K, but also in the paraelectric one at 90 K, if an external magnetic field (0.4 T ≤ µ 0 H ≤ 1.6 T) was applied ; in that case the magnetic structure changed from proper screw to longitudinal (for H z) or transverse conical (for H ⊥ z). 18 The activation of the electromagnon in E ω z polarized spectra was explained by the exchange striction, although the static electric polarization P⊥ z in hexaferrites comes from the inverse Dzyaloshinskii-Moriya interaction.…”